http://xml.apache.org/xalan-j/: Serializer to write out XML, HTML etc. as a stream of characters from an input DOM or from input SAX events. (The Apache Software Foundation) 
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 * to you under the Apache License, Version 2.0 (the  "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
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/*
 * $Id: XPathAPI.java 524807 2007-04-02 15:51:43Z zongaro $
 */
package org.apache.xpath;

import javax.xml.transform.TransformerException;

import org.apache.xml.utils.PrefixResolver;
import org.apache.xml.utils.PrefixResolverDefault;
import org.apache.xpath.objects.XObject;

import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.w3c.dom.traversal.NodeIterator;


The methods in this class are convenience methods into the
low-level XPath API.
These functions tend to be a little slow, since a number of objects must be
created for each evaluation.  A faster way is to precompile the
XPaths using the low-level API, and then just use the XPaths
over and over.
NOTE: In particular, each call to this method will create a new
XPathContext, a new DTMManager... and thus a new DTM. That's very
safe, since it guarantees that you're always processing against a
fully up-to-date view of your document. But it's also portentially
very expensive, since you're rebuilding the DTM every time. You should
consider using an instance of CachedXPathAPI rather than these static
methods.

See Also:
/**
 * The methods in this class are convenience methods into the
 * low-level XPath API.
 * These functions tend to be a little slow, since a number of objects must be
 * created for each evaluation.  A faster way is to precompile the
 * XPaths using the low-level API, and then just use the XPaths
 * over and over.
 *
 * NOTE: In particular, each call to this method will create a new
 * XPathContext, a new DTMManager... and thus a new DTM. That's very
 * safe, since it guarantees that you're always processing against a
 * fully up-to-date view of your document. But it's also portentially
 * very expensive, since you're rebuilding the DTM every time. You should
 * consider using an instance of CachedXPathAPI rather than these static
 * methods.
 *
 * @see <a href="http://www.w3.org/TR/xpath">XPath Specification</a> 
 * */
public class XPathAPI
{

  
Use an XPath string to select a single node. XPath namespace
prefixes are resolved from the context node, which may not
be what you want (see the next method).

Params:
  • contextNode – The node to start searching from.
  • str – A valid XPath string.
Throws:
Returns:The first node found that matches the XPath, or null.
/**
   * Use an XPath string to select a single node. XPath namespace
   * prefixes are resolved from the context node, which may not
   * be what you want (see the next method).
   *
   * @param contextNode The node to start searching from.
   * @param str A valid XPath string.
   * @return The first node found that matches the XPath, or null.
   *
   * @throws TransformerException
   */
  public static Node selectSingleNode(Node contextNode, String str)
          throws TransformerException
  {
    return selectSingleNode(contextNode, str, contextNode);
  }

  
Use an XPath string to select a single node.
XPath namespace prefixes are resolved from the namespaceNode.

Params:
  • contextNode – The node to start searching from.
  • str – A valid XPath string.
  • namespaceNode – The node from which prefixes in the XPath will be resolved to namespaces.
Throws:
Returns:The first node found that matches the XPath, or null.
/**
   * Use an XPath string to select a single node.
   * XPath namespace prefixes are resolved from the namespaceNode.
   *
   * @param contextNode The node to start searching from.
   * @param str A valid XPath string.
   * @param namespaceNode The node from which prefixes in the XPath will be resolved to namespaces.
   * @return The first node found that matches the XPath, or null.
   *
   * @throws TransformerException
   */
  public static Node selectSingleNode(
          Node contextNode, String str, Node namespaceNode)
            throws TransformerException
  {

    // Have the XObject return its result as a NodeSetDTM.
    NodeIterator nl = selectNodeIterator(contextNode, str, namespaceNode);

    // Return the first node, or null
    return nl.nextNode();
  }

  
 Use an XPath string to select a nodelist.
 XPath namespace prefixes are resolved from the contextNode.
 @param contextNode The node to start searching from.
 @param str A valid XPath string.
 @return A NodeIterator, should never be null.

Throws:
/**
   *  Use an XPath string to select a nodelist.
   *  XPath namespace prefixes are resolved from the contextNode.
   *
   *  @param contextNode The node to start searching from.
   *  @param str A valid XPath string.
   *  @return A NodeIterator, should never be null.
   *
   * @throws TransformerException
   */
  public static NodeIterator selectNodeIterator(Node contextNode, String str)
          throws TransformerException
  {
    return selectNodeIterator(contextNode, str, contextNode);
  }

  
 Use an XPath string to select a nodelist.
 XPath namespace prefixes are resolved from the namespaceNode.
 @param contextNode The node to start searching from.
 @param str A valid XPath string.
 @param namespaceNode The node from which prefixes in the XPath will be resolved to namespaces.
 @return A NodeIterator, should never be null.

Throws:
/**
   *  Use an XPath string to select a nodelist.
   *  XPath namespace prefixes are resolved from the namespaceNode.
   *
   *  @param contextNode The node to start searching from.
   *  @param str A valid XPath string.
   *  @param namespaceNode The node from which prefixes in the XPath will be resolved to namespaces.
   *  @return A NodeIterator, should never be null.
   *
   * @throws TransformerException
   */
  public static NodeIterator selectNodeIterator(
          Node contextNode, String str, Node namespaceNode)
            throws TransformerException
  {

    // Execute the XPath, and have it return the result
    XObject list = eval(contextNode, str, namespaceNode);

    // Have the XObject return its result as a NodeSetDTM.                
    return list.nodeset();
  }

  
 Use an XPath string to select a nodelist.
 XPath namespace prefixes are resolved from the contextNode.
 @param contextNode The node to start searching from.
 @param str A valid XPath string.
 @return A NodeIterator, should never be null.

Throws:
/**
   *  Use an XPath string to select a nodelist.
   *  XPath namespace prefixes are resolved from the contextNode.
   *
   *  @param contextNode The node to start searching from.
   *  @param str A valid XPath string.
   *  @return A NodeIterator, should never be null.
   *
   * @throws TransformerException
   */
  public static NodeList selectNodeList(Node contextNode, String str)
          throws TransformerException
  {
    return selectNodeList(contextNode, str, contextNode);
  }

  
 Use an XPath string to select a nodelist.
 XPath namespace prefixes are resolved from the namespaceNode.
 @param contextNode The node to start searching from.
 @param str A valid XPath string.
 @param namespaceNode The node from which prefixes in the XPath will be resolved to namespaces.
 @return A NodeIterator, should never be null.

Throws:
/**
   *  Use an XPath string to select a nodelist.
   *  XPath namespace prefixes are resolved from the namespaceNode.
   *
   *  @param contextNode The node to start searching from.
   *  @param str A valid XPath string.
   *  @param namespaceNode The node from which prefixes in the XPath will be resolved to namespaces.
   *  @return A NodeIterator, should never be null.
   *
   * @throws TransformerException
   */
  public static NodeList selectNodeList(
          Node contextNode, String str, Node namespaceNode)
            throws TransformerException
  {

    // Execute the XPath, and have it return the result
    XObject list = eval(contextNode, str, namespaceNode);

    // Return a NodeList.
    return list.nodelist();
  }

  
 Evaluate XPath string to an XObject.  Using this method,
 XPath namespace prefixes will be resolved from the namespaceNode.
 @param contextNode The node to start searching from.
 @param str A valid XPath string.
 @return An XObject, which can be used to obtain a string, number, nodelist, etc, should never be null.
 @see org.apache.xpath.objects.XObject
 @see org.apache.xpath.objects.XNull
 @see org.apache.xpath.objects.XBoolean
 @see org.apache.xpath.objects.XNumber
 @see org.apache.xpath.objects.XString
 @see org.apache.xpath.objects.XRTreeFrag

Throws:
/**
   *  Evaluate XPath string to an XObject.  Using this method,
   *  XPath namespace prefixes will be resolved from the namespaceNode.
   *  @param contextNode The node to start searching from.
   *  @param str A valid XPath string.
   *  @return An XObject, which can be used to obtain a string, number, nodelist, etc, should never be null.
   *  @see org.apache.xpath.objects.XObject
   *  @see org.apache.xpath.objects.XNull
   *  @see org.apache.xpath.objects.XBoolean
   *  @see org.apache.xpath.objects.XNumber
   *  @see org.apache.xpath.objects.XString
   *  @see org.apache.xpath.objects.XRTreeFrag
   *
   * @throws TransformerException
   */
  public static XObject eval(Node contextNode, String str)
          throws TransformerException
  {
    return eval(contextNode, str, contextNode);
  }

  
 Evaluate XPath string to an XObject.
 XPath namespace prefixes are resolved from the namespaceNode.
 The implementation of this is a little slow, since it creates
 a number of objects each time it is called.  This could be optimized
 to keep the same objects around, but then thread-safety issues would arise.
 @param contextNode The node to start searching from.
 @param str A valid XPath string.
 @param namespaceNode The node from which prefixes in the XPath will be resolved to namespaces.
 @return An XObject, which can be used to obtain a string, number, nodelist, etc, should never be null.
 @see org.apache.xpath.objects.XObject
 @see org.apache.xpath.objects.XNull
 @see org.apache.xpath.objects.XBoolean
 @see org.apache.xpath.objects.XNumber
 @see org.apache.xpath.objects.XString
 @see org.apache.xpath.objects.XRTreeFrag

Throws:
/**
   *  Evaluate XPath string to an XObject.
   *  XPath namespace prefixes are resolved from the namespaceNode.
   *  The implementation of this is a little slow, since it creates
   *  a number of objects each time it is called.  This could be optimized
   *  to keep the same objects around, but then thread-safety issues would arise.
   *
   *  @param contextNode The node to start searching from.
   *  @param str A valid XPath string.
   *  @param namespaceNode The node from which prefixes in the XPath will be resolved to namespaces.
   *  @return An XObject, which can be used to obtain a string, number, nodelist, etc, should never be null.
   *  @see org.apache.xpath.objects.XObject
   *  @see org.apache.xpath.objects.XNull
   *  @see org.apache.xpath.objects.XBoolean
   *  @see org.apache.xpath.objects.XNumber
   *  @see org.apache.xpath.objects.XString
   *  @see org.apache.xpath.objects.XRTreeFrag
   *
   * @throws TransformerException
   */
  public static XObject eval(Node contextNode, String str, Node namespaceNode)
          throws TransformerException
  {

    // Since we don't have a XML Parser involved here, install some default support
    // for things like namespaces, etc.
    // (Changed from: XPathContext xpathSupport = new XPathContext();
    //    because XPathContext is weak in a number of areas... perhaps
    //    XPathContext should be done away with.)
    // Create an XPathContext that doesn't support pushing and popping of
    // variable resolution scopes.  Sufficient for simple XPath 1.0 expressions.
    XPathContext xpathSupport = new XPathContext(false);

    // Create an object to resolve namespace prefixes.
    // XPath namespaces are resolved from the input context node's document element
    // if it is a root node, or else the current context node (for lack of a better
    // resolution space, given the simplicity of this sample code).
    PrefixResolverDefault prefixResolver = new PrefixResolverDefault(
      (namespaceNode.getNodeType() == Node.DOCUMENT_NODE)
      ? ((Document) namespaceNode).getDocumentElement() : namespaceNode);

    // Create the XPath object.
    XPath xpath = new XPath(str, null, prefixResolver, XPath.SELECT, null);

    // Execute the XPath, and have it return the result
    // return xpath.execute(xpathSupport, contextNode, prefixResolver);
    int ctxtNode = xpathSupport.getDTMHandleFromNode(contextNode);

    return xpath.execute(xpathSupport, ctxtNode, prefixResolver);
  }

  
  Evaluate XPath string to an XObject.
  XPath namespace prefixes are resolved from the namespaceNode.
  The implementation of this is a little slow, since it creates
  a number of objects each time it is called.  This could be optimized
  to keep the same objects around, but then thread-safety issues would arise.
  @param contextNode The node to start searching from.
  @param str A valid XPath string.
  @param prefixResolver Will be called if the parser encounters namespace
                        prefixes, to resolve the prefixes to URLs.
  @return An XObject, which can be used to obtain a string, number, nodelist, etc, should never be null.
  @see org.apache.xpath.objects.XObject
  @see org.apache.xpath.objects.XNull
  @see org.apache.xpath.objects.XBoolean
  @see org.apache.xpath.objects.XNumber
  @see org.apache.xpath.objects.XString
  @see org.apache.xpath.objects.XRTreeFrag

Throws:
/**
   *   Evaluate XPath string to an XObject.
   *   XPath namespace prefixes are resolved from the namespaceNode.
   *   The implementation of this is a little slow, since it creates
   *   a number of objects each time it is called.  This could be optimized
   *   to keep the same objects around, but then thread-safety issues would arise.
   *
   *   @param contextNode The node to start searching from.
   *   @param str A valid XPath string.
   *   @param prefixResolver Will be called if the parser encounters namespace
   *                         prefixes, to resolve the prefixes to URLs.
   *   @return An XObject, which can be used to obtain a string, number, nodelist, etc, should never be null.
   *   @see org.apache.xpath.objects.XObject
   *   @see org.apache.xpath.objects.XNull
   *   @see org.apache.xpath.objects.XBoolean
   *   @see org.apache.xpath.objects.XNumber
   *   @see org.apache.xpath.objects.XString
   *   @see org.apache.xpath.objects.XRTreeFrag
   *
   * @throws TransformerException
   */
  public static XObject eval(
          Node contextNode, String str, PrefixResolver prefixResolver)
            throws TransformerException
  {

    // Since we don't have a XML Parser involved here, install some default support
    // for things like namespaces, etc.
    // (Changed from: XPathContext xpathSupport = new XPathContext();
    //    because XPathContext is weak in a number of areas... perhaps
    //    XPathContext should be done away with.)
    // Create the XPath object.
    XPath xpath = new XPath(str, null, prefixResolver, XPath.SELECT, null);

    // Create an XPathContext that doesn't support pushing and popping of
    // variable resolution scopes.  Sufficient for simple XPath 1.0 expressions.
    XPathContext xpathSupport = new XPathContext(false);

    // Execute the XPath, and have it return the result
    int ctxtNode = xpathSupport.getDTMHandleFromNode(contextNode);

    return xpath.execute(xpathSupport, ctxtNode, prefixResolver);
  }
}